Diagnosis: Notalgia paresthetica
The location of the pruritic area and the patient’s clinical presentation led us to diagnose notalgia paresthetica. NP is a common dermatologic complaint characterized by unilateral pruritus that is medial or inferior to the scapula with dermatomal distribution.
The etiology of NP remains unknown, although it is thought to be a neuropathic itch caused by afferent nerve entrapment. The dorsal rami of the thoracic spinal nerves T2 to T6 are considered to be responsible for these symptoms. NP is not only a skin disease, but a cutaneous sign of an underlying spinal condition, including degenerative cervical spine disease.1-3
NP is a clinical diagnosis. There is typically a history of localized pruritus on the unilateral infrascapula area and there are few or no visible signs of disease. Patients frequently report a spider-bite sensation, prickly feelings, and/or an indescribable itch sensation. In addition, they may experience dysesthesia with diffuse mild burning, some surface numbness, and “under the skin” discomfort.
On physical examination, the patient may have a unilateral and ill-defined tan, pink, or hyperpigmented nonindurated patch on the infrascapular back that is a result of long-time scratching. Secondary skin changes such as lichenification, excoriations, eczema, xerosis, and infection often occur. Mild sensory alterations to light touch, vibration, and pin pricks may round out the clinical picture.1-3 Atypical forms of NP include localized pruritus on the upper back, neck, scalp, or shoulder.
Pruritus without other skin lesions can help pinpoint the Dx
The differential diagnosis for NP includes atopic dermatitis, contact dermatitis, drug eruptions, herpes zoster, idiopathic pruritus and systemic disease (such as renal, cholestatic, or hematologic pruritus, or pruritus associated with malignancy), tinea corporis, tinea versicolor, and xerosis.
Clues in the history. The chronic evolution of pruritus without other skin lesions, like vesicles or squamous areas, and the location of a hyperpigmented patch near the scapula region in a midlife patient, should prompt you to consider NP. A biopsy may show signs of post-inflammatory infiltrate of the papillary dermis with dermal melanophages.4,5
Although imaging tests are not required for a diagnosis of NP, basic cervical and possibly thoracic radiographs or magnetic resonance imaging (MRI) may be helpful in patients with symptoms of spine pain, tenderness, spasms, decreased range of motion, or any history of spinal trauma or injury. The images may reveal spinal disorders, including osteoarthritic lesions such as kyphosis, kyphoscoliosis, and vertebral hyperostosis.4
The exact cause of NP is unclear, but the evidence suggests that it results from damage to the cutaneous branches of the posterior divisions of the spinal nerves. This can occur by either impingement from degenerative changes in the spine or by spasms in the paraspinal musculature.2